Has anyone’s obsessive thoughts changed themes?

hello. i have been going through health scare obsessions for at least 5 years now and it terrifies me. i mainly fear of cancer. i have no reason to fear of cancer because it is not a predominant condition in my family. i have been to check ups for skin cancer and been told it was nothing which relieves me for a short period of time but then i start thinking of other cancer possibilities :( it doesn’t help that im a smoker to deal with the stress of adhd and ocd which just fuels the obsession of lung cancer. i know it would help my fear to stop smoking but thats easier said than done. i have only been a smoker for 3 years and its the only thing that helps right now. on top of this, my brain makes me believe that every intrusive thought i have WILL MANIFEST into existence just from thinking about it! this has scared me so much in the last 5 years and once i told my mum about it and she said "if you ever got cancer we would deal with it, its okay" but that didnt help it just made it worse and the possibility become more scarier! please help me.

Has anyone ever had an intrusive thought of thinking you’ve might’ve swallowed something dangerous and you can’t trust your own mind? And you feel like you need to go in to get checked out? Any advice or reassurance?

I have gotten maybe about 8 EKG’s within the lest 2 years? I’ve also gotten an echo done, and I got a heart monitor to track my heart over the course of maybe 2 weeks, back last year. Even though I have been to the emergency room so many times because of panic attacks that I thought were heart attacks, and went with a Cardiologist I still obsess and worry. I always think that I am going to develop some kind of heart problem after getting the tests done. Like if they’re just suddenly going to appear/my heart will suddenly have an issue. I especially get nervous when the pain is in the center of my chest + I get a tight feeling like I have pressure on my chest and can’t breathe completely. Please someone share their experience of how they controlled their health anxiety, especially if it’s related to this.